Flexible intermediate bulk containers are increasingly employed in cargo handling and transporting situations, especially for the carriage of particulate or pulverulent material. A typical FIBC will be manufactured from a fabric woven from polyolefin tapes and have integral lifting loops. Examples of such containers are described in UK patent numbers 1 591 091 and 2 063 816. FIBC's have to meet various national and international safety standards; for example, it is normal to require 5:1 safety ratio, that is an FIBC rated at one tonne should not break under loads of less than five tonnes.
Some products are less free flowing than others and can tend to clog (variously known as to "bridge" or "rat hole" in the industry) during emptying of an FIBC. It has been proposed to produce FIBC's with a cone shaped base to facilitate emptying of such products but such FIBC's are relatively expensive both because they require more material and because different manufacturing methods must be employed for relatively small numbers of bags.